Why humans have an Appendix

As someone who had their appendix burst a few years ago, I have wondered why we have these organs.  The traditional view has been that the appendix was a residual organ that was no longer used.  From ABC News:

The researchers say it acts as a safe house for good bacteria, which can be used to effectively reboot the gut following a bout of dysentery or cholera. 

The conventional wisdom is that the small pouch protruding from the first part of the large intestine is redundant and many people have their appendix removed and appear none the worse for it. 

Scientists from the Duke University Medical Centre in North Carolina say following a severe bout of cholera or dysentery, which can purge the gut of bacteria essential for digestion, the reserve good bacteria emerge from the appendix to take up the role. . . .